G.f. A(x) defined by A(x) = 1 +x*A(x) +x^2*A(x)^2 +3*x^3*A(x)^3.

Terms

a(0) =1a(1) =1a(2) =2a(3) =7a(4) =21a(5) =66a(6) =228a(7) =799a(8) =2843a(9) =10357a(10) =38278a(11) =143012a(12) =539980a(13) =2056848a(14) =7892496a(15) =30483351a(16) =118416903a(17) =462348219a(18) =1813410078a(19) =7141608015a(20) =28229040165a(21) =111956307486a(22) =445374729396